The present invention relates to wireless communications, and more particularly to the selection of a primary control signal bus for cascaded radio heads that have buffered communications links between radio heads.
In today""s wireless communications environment, it is not uncommon to have localized wireless telephone systems, such as might be installed in a building or on a campus, that are designed to cover a relatively small geographic area. A typical physical configuration of such a localized system includes a central cabinet connected to a plurality of radio heads. The central cabinet (located at the site/premises) includes regional processors and signaling terminals (also known as xe2x80x9ccontrol interfacesxe2x80x9d or xe2x80x9ccontrol interface unitsxe2x80x9d) that oversee communications with the relevant Mobile Switching Center (MSC) and with the corresponding regional processors. The signaling terminals communicate with the regional processors over two or more control signal buses within the control cabinet. The regional processors in turn communicate with the radio heads, typically over a suitable T1 or E1 link. The radio heads are typically arranged in a cascaded fashion, forming a chain of radio heads, with only the end radio heads of the chain directly connected to the central cabinet.
Typically, each radio head in the chain is physically located a substantial distance from the next radio head, such as up to 1000 meters apart. Because of this physical separation, it is common to employ error detection and correction schemes to the transmissions between the successive radio heads. Use of such error correction schemes means that data from the central cabinet to a given radio head, say the third radio head, is buffered at the central cabinet for error correction purposes, sent to the first radio head in the chain, buffered again at the first radio head for error correction, sent to the second radio head, and buffered yet again at the second radio head for error correction, before being sent to the third radio head. There can thus be a significant time delay between the central cabinet sending the information and its receipt at the desired radio head. This time delay, sometimes referred to herein as a propagation delay, is generally a function of the error detection and correction schemes employed, the processing speed of the relevant processor(s), the distance between radio heads, and the number of xe2x80x9chopsxe2x80x9d between the central cabinet and the desired radio head.
When installing (or removing) radio heads in a localized system described above, it is necessary to decide which control signal bus each regional processor should consider as its primary bus. Generally, this means that the responsible technician must perform some function that assigns each regional processor to one of the plurality of control signal buses; typically, this involves assigning the regional processor to bus A or bus B based on the physical positioning of the corresponding regional processing board within the central cabinet. Because there is generally a one-to-one relationship between regional processors and radio heads, with a given regional processor controlling a given radio head, this results in the radio heads being effectively assigned to bus A or bus B based on the location of the corresponding regional processing board within the control cabinet. However, such bus assignments sometimes result in unnecessarily long propagation delays for a given radio head.
According to the present invention, selection of the primary control signal bus to use for a given radio head is based on propagation delay to the relevant radio head. A wireless communications system may include a plurality of radio heads cascaded in a chain and at least first and second control interfaces connected to the chain and supplying control information thereto. The communications between radio heads employ buffered error correction, resulting in store-and-forward propagation delay. A plurality of virtual control signal busses are established connecting the control interfaces to the plurality of radio heads, including at least a first virtual bus connecting the first control interface to the plurality of radio heads and a second virtual bus connecting the second control interface to the plurality of radio heads. The propagation delay from the first control interface to a first radio head over the first virtual bus is determined. Likewise, the propagation delay from the second control interface to the first radio head over the second virtual bus is determined. Thereafter, the first radio head determines which control signal bus, from amongst a plurality of virtual busses, to select as its primary control signal bus based on the respective propagation delays between the first radio head and the first and second control interfaces.